Numerous industrial and product applications require complex generally tubular shapes. For example, in the vehicle industry, vehicle components, such as vehicle frame rails, unibody components, suspension members, engine cradles and instrument panel support beams may be of tubular construction, where the component is often formed from a tubular member to define a generally rectangular cross-section. Tubes of a given diameter, for example, of the larger size required for vehicle applications, may buckle, stretch, wrinkle, and/or ripple if not sufficiently supported during the bending and forming processes. Forming of such tubular components in a conventional, e.g., standard mechanical or stamping press presents problems with sufficiently deforming the workpiece, which is provided as a tubular member, to form or flow the workpiece to fill the recesses of the die cavity defined by the upper and lower die, without collapsing, buckling or wrinkling the tubular structure of the workpiece.
Hydroforming processes have been developed to form complex tubular components by, generally, placing a tube or workpiece between a pair of dies such that as the dies merge, the ends of the tubular workpiece are sealed with a pair of sealing units. The workpiece is filled with a fluid, typically water or a water-glycerin mixture, which is then pressurized. Pressurizing the fluid within the workpiece results in forming and expanding the tube to conform to the cavity shape, wherein the pressurized fluid acts as a mandrel to support the interior surface of the tubular workpiece to prevent collapse or wrinkling of the tubular structure while the workpiece is deformed to conform with the configuration of the die cavity. The sealing units are removed prior to releasing the workpiece from the hydroforming press, and the hydroforming fluid is drained from the formed part. The primary disadvantages of hydroforming are cost and cycle time, the required use of specialized hydroforming presses equipped with hydraulics and high pressure pumps, extended cycle times for pressurizing and draining each workpiece, hydraulic fluid tanks and fluid management systems, and high maintenance cost and time. Additionally, some part configurations may require a pre-form operation of bending the workpiece using a bender and mandrel prior to forming the part using a hydroforming process.